The present invention relates to an air flow rate meter, and more particularly a thermal air flow rate meter for use in controlling an automobile engine.
The task of decreasing harmful exhaust gas emissions from automobile engines is extremely important, to protect the natural environment and save resources. For this purpose, it is indispensable to control the fuel supply and ignition timing of the engine precisely. To accomplish this, information concerning the flow rate at which air is sucked into the engine is essential. Thus, the demand for a thermal air flow rate meter capable of directly and accurately measuring an air flow rate has increased. For an automobile in particular, a highly precise air flow rate determination must be made in its operating environment, including a temperature range which may vary by as much as -40.degree. C. to 120.degree. C.
In order to maintain a highly precise air flow rate measurement in such an environment, the ambient air temperature must be compensated accurately. For example, Japanese Laid-Open Patent 1-274016 uses a microcomputer to control a heating temperature of a heat generating resistor for this purpose. However, since this system provides a voltage output in the form of a pulse signal, which is not compatible with current applications systems, the hardware must be changed.
Also, with prior art devices, it is difficult to detect the air flow rate with high accuracy over a wide temperature range because the temperature is controlled by intermittently heating the air.
It is therefore an object of the present invention to provide an air flow rate meter and air flow rate detection method capable of detecting an air flow rate in a wide temperature range.